Electromagnetic sound reproducer



Aug. 28, 1945. w DE VERTER 2,383,594

ELECTROMAGNETI C SOUND REPRODUCER Filed Jan. 2, 1943 Patented Aug. 28,1945 zssssai UNITED STATES PATENT oFjFicE fmacraomcns'r 'ffsi rxsnanraonvcm I I Ap lleat lonlzlnz'i 2,-( r;:s1,::i:iwo; 411,132.

This invention relates'to sound reproducers or loud speakers, moreparticularly to electrodynamic sound reproducers in which a movabledynamic or voice coil, excited with sound-representlngor voice currents,isprcvlded' for inter-' action with anintense unidirectional magneticfield, and the invention has for an-biect the provision of improvedsound character.

In, the usual radio receiveror electric piano graph adapted foroperation on commercial alternating current, the field producing windingof the electrodynamic sound reproducer'assoreproducers 01 this ciatedwith such apparatus is excited with unidirectional pulsatingcurrentpsuch as may be obtained from the rectifier circuit utilized forsupplying the plate and grid energy to the amplifier tubes or thereceiver or phonograph. Thefluctuations or periodic variations of themagneticfield produced by such excitation have been found to produce, byinteraction with the,

dynamic coll, an undesirably intense and annoying hum in the loudspeaker.

In order to minimize or substantially eliminate this undesirable hum, ithas heretofore been i proposed to provide such sound reproducersor -loudspeakers with a second or bucking coil dis-' posed in the magnetic fieldand connected di-- rectly in series with the voice coil and the sourceof sound-representing or voice currents. This minimizing means introdynamic type.

In' carrying out'the invention in one form, a

loud speakersof the eiec loud speaker is provided having" the usualfield,

producing winding and a or voice coil disposed in the magnetic field andenergized from a suitable source of sound-representing currents.

as to'oppose and minimizecurrents induced in the voice coil byfluctuations-in: the strength of the magnetic field. The .parallelbucking coil, which may be designed so as to carry only a smallcomponent of the sound-representing currents supplied to the voice coil,may be iormedtoi second series coil is 01' opposite polarity to the 7voice coil, and therefore tends to produce in the voice coil voltagesopposite in phase to those induced directly in the voice coil bythefiuctua- I tions of the magnetic field.

While inmost respects electrically satisfactory, .mechanicaldiificulties are encountered in the economic construction and properlocation of such series bucking coils. Ordinarily such series coils arewound on separate forms or tubes and may be placed either over the coreoi the horn Iii, a field winding ii, a dynamic or voice very fine gaugewire. and the area occupied thereby and the costs of fabrication andmaterials are considerably less than for the heretofore known seriesbucking coils. 7

- For a more complete understanding of the invention, reference shouldnow be had to the drawingin which the single figure is a diagrammatic'representation of a sound reproducer or loud speaker embodying thepresent invention.

In the drawing, the invention is shown as embodied in a loud speakercomprising the usual coil i2, and a bucking coil ll. Since the magnetcircuit or the sound reproducer is entirely conventional, only theelectrical circuits have beenshown.

loud speaker, or inside of the field winding, or-

around the outer periphery of the field In any event, the series coil,which must carry all of the voice or sound-representing currentssupplied to the dynamic, coil, must be formed of relatively heavy wire,"and thus difiiculties are introduced into fabrication and excessivecostsare encountered. In addition, the heavy wire I series-coil takes upspace which could otherwise be devoted to better use in constructing theloud speaker. Accordin ly. something is yet to be desired in providingcompact, inexpensive and electrically satisfactory .loud speakers ofthis character, and it is a further object 0'! this in- Thefield windingII is connected, as shown,

to a pair of terminals M which may represent a sourceoi periodicallyfluctuating unidirectional current such as may be obtained from theusual rectifier circuit. .The voice coil I2 is connected to be suppliedwith sound-representing currents from the secondary winding II ot'asuitable transformer I, the primary winding I! of which is connected tosuitable terminals II which may, 7

. ior, example, be the output terminals of an ampliiier system such asis contained'in a radio receiver or an electric phonograph. The voicecoil I2 is of course disposed in the intense magnetic field produced bythe winding l I, so that upon the dew oi sound-representing currentsthrough the voice cell it, movement thereoi will be producedandthevoice-coilmaybaconnected in anysuitable manner to the diaphragm oithe-horn Ill.

small component of the voice-representing currents from the transformerwinding l5 flows through the bucking coil I3.

In addition to the parallel circuits the two coils l2 and I3 constitutea local-series circuit which may be traced from one terminal of thewinding l3, through the conductors l9 and 20, the coil l2, and theconductorsZl and 22, to the opposite terminal of the coil l3. The coilsl2 and I3 are, as previously indicated. of opposite polarity so that theinductive effect of the magnetic fieldon these coils tends .to produce,in the two coils of the local series circuit, voltages and currents ofopposite polarity. Thusthe direction of the voltages and currentsinduced inthe coil 13 is represented in the drawin by the'broken arrowsextending about the local series circuit, while the direction oi thevoltages and currents induced in the coil 12 is'represented by the solidline arrows extending about the local series circuit. v

Byproperly adjusting the locations of the respective coils l2 and Handthe electricalcharacteristics of each coil, it is possible substantiallyto eliminate or greatly minimize the flow of current inth'e localseriescircuit due to the inductiv'e eflect of the fluctuations in the magneticotherwise appear. in the hom ID of the loud i speaker. is reduced to asatisfactorily low value.

While I have shown a particular embodiment of my invention. it will beunderstood, of course, that I do not wish to be limited thereto sincemany modifications may be made, and I, therefore, contemplate by theappended claims to cover any such modifications as fall within the truespirit and scope of my invention. 1

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. In an electrodynamic sound reproducer, the combination of a fieldwinding energized by unidirectional current to produce a magnetic field,

a source of sound representing current, a dynamic coil connected acrosssaid source and disposed in said magnetic field, and a bucking coildisposed in said field and connected across said dynamic coil inparallel relation thereto with respect to said source to form a localseries circuit includin said two coils, said bucking coil anddirectional current to produce a magnetic field,

a source of sound representing current, a dynamic coil connected acrosssaid source and disposed in said magnetic field,'and a bucking coildisposed in said ffield and connected acros s said dynamic coil inparallel relation thereto with respect to said source tofformfa localseries circuit including said two coils, said bucking coil beingarranged to-produce in said local series circuit, by the inductiveefiect thereon of variations'in the strengthiof said field potentialsopposite in a polarity to the potentials induced in said dynamic coil bysaid variations.

WALTON on ,VERTER.

